Abstract: A tonometer for measuring the intraocular pressure of an eye featuring an acoustic signaling system for determining the beginning of a pressure measurement. The acoustic system includes a consumable cap having a pair of annular raised surface portions spaced by a recessed area. The raised surface portions provide an eye-engaging surface at the face of the tonometer. A pressure transmitting plunger concentrically suspended between the raised surface portions by a plurality of spider arms combines with the eye-engaging surface to provide a contour which complements a shape of an eye. The recessed area is open along the eye-engaging surface, yet defines a generally enclosed volume when full tonometer-to-eye contact is made. Spaced apart inlet and outlet apertures within the recessed area permit channeling of an acoustic signal to and from the recessed area. Prior to proper coupling of the tonometer to an eye, a substantial amount of the energy of the acoustic signal is lost to free air.